This text provides a concise and clear introduction to the molecular components which can be used by cells to signal either to each other, or to signal from their surface to their interiors. The text takes a generic approach, describing components of animals, plants and prokaryotes, and as such is not restricted to any particular field. Cell Signalling begins with an overview chapter, exploring concepts applicable to all areas of the subject. Subsequent chapters concentrate on the use of extracellular signals and their perception and then focus on intracellular components, such as G proteins, cAMP, inositol metabolism and calcium. Final chapters discuss free radical signals such as nitric oxide and hydrogen peroxide, and give examples of signalling pathways, such as those induced by insulin.